I use a simple bbq grill propane tank, with an adapter fitting to connect to the generator inlet. you need a primary regulator, like most RV propane tanks use. make sure to stand it up with valve on top. as you want vapor only.
The 2.5 KV Onan LP set was used for about 20 yrs, then replaced a few years ago by the HGJBB model. They have completely different control systems, and knowing which you have would be helpful in diagnosing problem.
And, I agree....I hate to see these come to shop, as usually are mounted under vehicle, behind rear axle, and you cant do anything except basic service...and that is difficult. I have never had a customer that said they ever would crawl under the vehicle to even check oil
